Daily deal site Groupon is offering the Samsung Focus Flash with Windows Phone 7.5 “Mango”, for $159 shipped. The phone is banded to use AT&T “4G” HSPA+ networks, but also can work on T-Mobile.

In fact, with T-Mobile rebanding some spectrum to support HSPA+ from iPhone, other unlocked devices such as the Focus Flash will also be able to take advantage of HSPA+ on T-Mobile, though not with the coverage levels of a standard T-Mobile device. Unfortunately, T-Mobile does not offer a fine-grained coverage map that shows the 850/1900 MHz UMTS/HSPA network overlay in detail, so your mileage will vary.

Regardless, this is an excellent deal for those that want a Windows Phone on unlimited prepaid. Combined with an Straight Talk AT&T SIM card, you can leverage unlimited talk, messaging, and data for $45/month with Windows Phone 7.5. And, the Focus Flash is the most likely of Samsung’s Windows Phone 7-era devices to get upgraded to the swan song Windows Phone 7.7 release, though Samsung has not commented on if any of their Windows Phones will be upgraded to 7.7.

Groupon is also offering free returns for purchasers who are on the fence. It also is not clear if the firmware is unlocked/unbranded, so some Windows Phone features such as tethering may not be fully accessible. Unlike Android, it isn’t possible to sideload in an alternative tethering app, should Microsoft’s tethering be blocked by an AT&T tethering plan server/check.

Christopher Price is the Founding Editor of PhoneNews.com. Today, he leads the team building Console, Inc. - a new kind of Android™ device. He still likes to pontificate... a lot. You can visit his personal blog at ChristopherPrice.net.